Research firm IDC today updated its tablet shipments forecast to reflect the growing popularity of low-cost tablets coming from the Android camp.

IDC now predicts that Android tablets will overtake the iPad in terms of volume during the course of 2013.

The firm pegged Apple’s share of the global tablet market in 2012 at 51 percent, with Android-driven tablets accounting for 41.5 percent of shipments. The new forecast calls for Android’s share hitting a peak of 48.8 percent in 2013, mostly at the expense of Apple’s iOS predicted to drop down to 46 percent this year.

But why stop there, IDC futurists project tablet shipments nearly four years into the future: in 2017, they expect Android to own 46 percent of the market, with the iPad dropping to a 43.5 percent share. As we know all too well, Apple isn’t one to blindly pursue market share, as evident in smartphones where it captures three-quarters of industry profits with barely one-tenth of total handset shipments…

According to IDC data, tablet vendors will ship 190.9 million units this year, up from IDC’s previous forecast of 172.4 million units. By the end of 2017, IDC predicts upwards of 350 million tablet shipments.

In case you didn’t get the memo, mainstream buyers are choosing sub-8-inch tablets, with one in every two tablets shipped this quarter below eight inches in screen size.

“In terms of shipments, we expect smaller tablets to continue growing in 2013 and beyond” said IDC analyst Jitesh Ubrani said. “Vendors are moving quickly to compete in this space as consumers realize that these small devices are often more ideal than larger tablets for their daily consumption habits.”

The researchers project that long-term, Windows-based tablets will steal some share from both Google and Apple as these devices grow from just one percent of the market in 2012 to a 7.4 percent share in 2017.

Interestingly, the research firm expects Windows RT growth to remain below three percent during the forecast period.

“Consumers aren’t buying Windows RT’s value proposition, and long term we think Microsoft and its partners would be better served by focusing their attention on improving Windows 8,” IDC said.

Dedicated e-readers such as Amazon’s Kindle will be under lots of pressure as inexpensive smaller tablets gain ground, reducing the e-reader category by an average of fourteen percent between 2013 and 2016. E-reader shipments peaked in 2011 at 26.4 million units and declined to 18.2 million units in 2012.

IDC now expects e-readers to grow only modestly in 2013 and 2014, before beginning a “gradual and permanent decline” beginning in 2015.

I must admit I’m not fond of IDC peering into the crystal ball. For God’s sake, it just amended tablet shipments estimate because these researchers lacked the wisdom to assume that tweener tablets would become popular with ordinary buyers due to attractive price points.

2017 is three years and nine months from now. Three years and nine months ago the tablet market was non-existent. I think neither IDC nor any other research firm has the database, the knowledge and wisdom to accurately predict what the market will look like in such a long timeframe.

And now they’re predicting 2017. Anything can – and will – happen in the next few years.

IDC in November 2012 said that in the race to win the tablet market, Android gained tablet market share during the September quarter while Apple slowed. A month later, the research firm in another report predicted the iPad would maintain its market share dominance throughout 2016.

With tablets now comprising 25 percent of PC sales, it’s of course imperative that Apple remains the market leader, but nobody in their right mind is expecting the company to keep half the market to itself indefinitely – that’s just not how the market works.

Even though Apple was first to market a mainstream tablet which caught competitors on the wrong foot, that gap has been narrowing, even more so with the release of Android 4.0 and Amazon / Google entering the tablet arena with own products.

That’s to be expected in any industry.

Price-wise, Apple’s most affordable iPad is the $329 iPad mini. With everything below $329 up for grabs, rivals are seizing their chance with sub-$200 tablets. And as the market matures, less-pricey tablets will take off in a big way in emerging markets like China, India, Russia and Brazil.

Again, even if Android vendors collectively outship Apple’s iPad (and how could they not?), guess who will be reaping most profits off these devices?

And unlike smartphones, the iPad has an important app advantage, with more than 300,000 applications designed specially for it. Though we lack the official numbers, that number is certainly significantly lower on Android as most apps for Android tablets are basically oversized mobile phone apps.